1. Field of the Invention
The present invention relates, generally, to the field of printing press apparatus and, more particularly, to paper perforating and scoring devices directly associated with continuous web printing presses.
2. Prior Art
Expensive, high speed printing presses are commonly used by commercial printing companies. Many such printing presses are fed from large rolls of paper on a continuous strip of paper known in the art as a "web". The presses are generally known in the industry as web presses and may cost between two and three million dollars each.
A web press, typically, requires the use of an automated web cutting and folding machine to receive the printed web at high velocity. The cutting and folding machine automatically cuts the web into sheets and folds the sheets one or more times into folded articles referred to as "signatures". The signatures may be sold as produced or they may be delivered to other machines which stitch or bind the signatures into books, booklets, magazines, or the like. Such signature folding machines are very expensive.
Consequently, it can be appreciated that the presses and folding machines must be capable of operating for extended periods of time at very high speeds in order to be cost effective in the production of finished signatures. However, problems which significantly limit folder and, hence, press speed are commonly associated with the signature folder operation.
One of the significant problems is that many commonly used signature folders are constructed to perform two or more sequential paper folding operations. In a first folding operation, the web is inserted along a fold line between rollers which make the fold and cut the web. The folding problems associated with the first folding stage are no greater than might be expected in high speed folding operations inasmuch as the web is still intact and taut when the first fold is made. However, any subsequent fold is, generally, accomplished by a blade striking the already folded, and severed, sheet along a second fold line and pushing the new fold between a second (and subsequent) pair of rollers. This folding process can be repeated several times.
One way to overcome the problems associated with signature folders is to use two separate signature folders, each of which is operated at half the press speed. Although signature production rates can be substantially increased, equipment and overhead costs are also increased significantly.
Recognizing the above, press and folder manufacturers have attempted to reduce the second stage folding problems by scoring the web along the second fold line before the first fold is made. For such pre-fold scoring, the web passes through a web scoring apparatus in the signature folder upstream of the first folding stage. The scoring apparatus typically includes a circular scoring blade mounted on one side of the web and a resilient roller mounted on the other side of the web. As the web advances between the rotating scoring blade and roller, a longitudinal indentation or groove is pressed by the blade into the web along the subsequent second fold line. However it has been found that the longitudinal pre-fold scoring of the web does not significantly reduce second stage folding problems and may actually increase same. That is, uniform, pre-fold web scoring scores only part of the sheet in the correct direction for second stage folding. The other part of the sheet is actually scored in the wrong direction for the second fold.
For these and other reasons, a pre-fold web scoring apparatus for use in signature folders and which scores the web in alternating directions corresponding to the second fold direction for each layer of the paper is desirable. Such a device is referred to as a "skip-scorer" and is described in U.S. Pat. No 4,524,962.
The skip-scorer of the prior art includes a pre-fold scoring apparatus through which paper is fed prior to being folded into signatures. The scoring means includes first and second rollers each having separate scoring and resilient abutment portions configured for causing prescribed lengths of the paper to be scored in alternating directions thereby to facilitate the folding thereof. The scoring means are mounted in the path of paper travel so as to enable scoring of the paper before the paper enters the first folding stage.
Preferably, the scoring means comprise first and second complementary-shaped scoring rollers, each of which has alternating peripheral scoring blades and resilient roller portions having arc lengths equal to the length of the fold. The first and second scoring rollers are rotatably mounted upstream of the first folding stage and in the path of paper travel. The two scoring rollers are mounted in mutual, peripheral rolling contact so that the scoring blade portion of each contacts the resilient roller portion of the other as the scoring rollers are rotated. Portions of the paper passing between the scoring rollers is thereby scored in one direction and other portions of the paper are scored in the opposite direction so that each layer of paper to be folded in multiple folding stages is scored in the correct folding direction.
To enable proper scoring for different weights of paper, the scoring blade portions of the first and second scoring rollers are constructed so that each comprises a scoring blade having an arcuate scoring edge which bears upon the resilient roller portion. However, this operation tends to cause the resilient portion of the rollers to wear down. When the resilient portions wear down, the scoring does not occur accurately. Thus, it is necessary to replace the resilient portion of the roller. This replacement is time consuming and expensive in that the roller must be removed from the press and a new roller inserted. Replacement of the resilient surface pads on a roller is, generally, not satisfactory wherein the entire unit must be replaced. Consequently, a more economical arrangement for scoring and/or perforating is desirable.